Process of recovering acid



H. G. STONE.

PROCESS OF RECOVERING ACID.

APPLICATION FILED 1UNE4, 1919.

1 3 1 4,7 6 5 Patented Sept. 2, 1919.

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PROCESS OF RECOVERIIN'G ACID.

Specification of Letters Patent.

Patented Sept. 2, 1919.

Application filed June 4, 1919. Serial No. 301,601.

To all whom it may concern:

Be it known that I, HERBERT G. STONE, a citizen of the United States, residing .at Wytheville, in the county of Wythe and State of Virginia, have invented certain new and useful Improvements in Processes of Recovering Acid, of which the following is a specification.

This invention relates to processes of recovering acid; and it comprises a method of recovering acetic acid from vapors of tanning extracts undergoing concentration in multiple effect apparatus, as well as of re-. covering other volatile acids from other liquids, wherein such vapors are passed through a casing without material impairment of their heat or velocity and while in such casing are contacted with sprayed alkali solution; and it further comprises as a new organization of apparatus elements a pair of multiple efiect evaporators with a special casing located in the vapor line between the two, such casing being provided with spraying means for alkali; all as more fully hereinafter set forth and as claimed.

Ordinary commercial tanning extracts are made by leaching or extracting various woods and barks in well known ways, and afterward evaporating down the watery solutions so obtained'to a convenient commercial density,'or even to dryness. In evapcrating,

for the sake of econom offuel and to avoid damaging the materlals by high heat, it is'usual to employ what are known as multiple effect evaporators, evaporators working under vacuum and so connected that the vapors of one are used in the heating coils or heating elements of another to produce evaporation therein; the second one, of course, always operating under lower pressure than the one in which the vapors originated.

In all extracts, or practically all, of. vegetable materials of the nature of wo s and barks there is found a small amount of free acetic acid. Its amount is rarely great but there is usually some. In evaporating these extracts, because of the peculiar relations of acetic acid. to water in distillation, acetic acid occurs in the vapors throughout the concentration. The concentration in any given extract is not over one-tenth per cent.

. or so, although at times it is hi her, but in the aggregate in an ordinary actory this small percentage of ac1d.in the liquor means a, .considerablc amount in the course of a day. The amount is worth recovering and, furthermore, the presence of acid in the vvapors renders the vapors and condensates velocity of travel. It would naturally be inexpedient in running two connected pans, the vapors from the one heating the other, to place any substantial impediment in the path of the vapors between the two.

I have however found that I can recover the acetic acid from the vapors of evaporation by the use of several expedients without 1n any way impairing the capacity or operation of the evaporators. To this end I. place in the vapor line a casing of sufiiciently great cross section to afford not only free passage of vapors, but slow down temporarily their passage somewhat without placing friction in the line. Within this casing, I mount means for sprayin alkali; this means being connected to suita le pumping means so that the liquor deposited in the bottom of the casing, after being sprayed may be sent back to the spraying means. In recovering acetic acid from bark extracts I customarily use lime as the alkali, producing calcium acetate. Soda may be used for neutralizing but is open to the objection that more or less tanning material usually passes forward with the vapors by entrainment and soda forms soluble compounds with the tannins. By using lime in the manner described, that is, with a cyclic circulation to and through the neutralizing casing and spray nozzle therein, I obtaln a calcium acetate solution of high grade; the salts produced from it by further evaporation frequently analyzing as high as 99 per cent. calcium acetate. It is a much higher grade preparation than the usual crude acetate from the wood distilling plants; being white or reddish white in appearance and susceptible of solution, evaporation and reconcentration to give a chemically pure acetate. Because of the circumstances within the neutralizing casing, the solution may be withdrawn in a saturated condition or of a less concentration as may be desired. In operating under the present process a charge of "alkali may be placed the system and cireffects, as in evaporating sulfite waste liquors. p

In the accompanying illustration I have shown, more or less diagrammatically, certain apparatus within the present invention and useful in the performance of the described process. In this showing the view is a central vertical section, certain parts being in elevation. In this showing elements 1 and 2 are fragmentally shown multiple efi'ect pans of any usual construction provided with vapor connections 3 and 4: respectively. As shown, these are represented as the first and second effects (inorder of decreasing temperature) ofa; mul- .'tiple effect assemblage.- Between the two effects and receiving vapor from the vapor outlet from the first is an acid catcher indicated as a whole by 5. As shown, entering vapors pass through conduit 6 into a somewhat expanded spraying chamber 7, having a perforated spray plate 8 mounted therein. Below this expansion is downtake 9, shown as ending immediately above a series of stationary vanes 10, mounted on spider 11. These vanes serve to give awhirling motion to the mixture of vapors solution). As shown the casing is of considerably greater diameter than the vapor line proper, to provide for a certain amount of slowing up of vapors passing therethrough. At the top the casing is connected to, vapor line 12, leading to the inlet for heating vapors of the next efl'ect. Mounted, onthis vapor line is a catch-all 13-with conduit 152 leading liquid back to: the acid casing.,At, the bottom of the acid casing is a valved liquid outlet 15 connected to centrif- .ugal-pump 16. Entering this is a valved and liquid (acid alkali inlet 17. From the centrifugal pump on thepressure side conduit 18 'leadsback into the casing, terminating in an upwardly directed spray nozzle 19. This conduit is valved at 20 and is provided with valved outlet 21 for acetate solution.

In the use of this apparatus, the vapors entering pass into the expanded chamber in line 6' where they are met by a spray containing lime. This finely divided spray causes intimate contact of the alkali with the vapors and effectually removes acids from the vapor without condensation of the vapor. The drops of liquid comin the perforated plate and thence downward to the bottom of the casing for removal by the pump. Vanes 10 give a whirling motion to the vapor, drops of liquid to ing. The steam coil 22 serves to maintain temperature in event there is too much cooling effect due to expansion of the vapors.

What I claim is I 1. The process of recovering acetic acid from the vapors of vegetable extracts undergoing evaporation in multiple eflect apparatus which comprises intimately contacting alkali with the vapors passing from effect to effect.

2. The process of recovering acetic acid from the vapors of vegetable extracts undergoing evaporation in multiple efi'ect apparatus which comprises spraying lime into the vapors passing from effect to effect.

3; In the operation of multiple efi'ect evaporators, the process which comprises sprayin alkali into the vapors passing between e ects.

from the spray nozzle pass downward t rough throwing any entrained the periphery of the cas 4. The combination -,with multiple efl'ect apparatus of vapor treating apparatus located between the inlet of one effect and the material while the vapors are passing from one effect to another. v

In testimony whereof, I afiix my signature hereto.

' HERBERT G. STONE. 

